The present invention relates to a solid article that includes an oxygen scavenger, and includes or is proximate to a luminescent compound that indicates the absence of oxygen dissolved in the solid article, particularly a polymeric solid such as a film that can be used to package an oxygen sensitive product, such as a food product. The article and associated method is useful as a real time or very rapid quality assurance check to verify oxygen scavenger activity during package assembly.
Oxygen spoils many products. Foods, beverages, pharmaceuticals, medical devices, corrodible metals, analytical chemicals, electronic devices, and many other products may perish or experience diminished shelf life when stored too long in the presence of oxygen. To combat this problem, manufacturers of packaging materials have developed packaging materials and systems to protect these products by providing a package environment, or xe2x80x9cheadspacexe2x80x9d, with reduced oxygen levels.
In many cases, the low oxygen level that can be obtained with these packaging systems is still insufficient to provide the desired shelf life. In these cases, packagers find it advantageous to include an oxygen scavenger within a low oxygen modified atmosphere package (MAP) or a vacuum package (VP). Packaging materials that include oxygen scavengers have grown increasingly sophisticated in recent years. For example, Speer et al. have developed clear, multi-layered packaging films that incorporate an oxygen scavenging composition within its layers. See U.S. Pat. Nos. 5,529,833, 5,350,622, and 5,310,497, the contents of which are incorporated herein by reference in their entirety. In this regard, see also Babrowicz et al. U.S. Pat. No. 5,993,922, also incorporated herein by reference.
For oxygen scavengers made from ethylenically unsaturated hydrocarbons and their functional equivalents, oxygen scavenging activity is triggered with actinic radiation, typically in the form of ultra violet (UV-C) light. For details on preferred methods for activating such oxygen scavenging compositions at point of use, see Speer et al., U.S. Pat. No. 5,211,875, Becraft et al., U.S. Pat. Nos. 5,911,910, and 5,904,960, and co-pending applications U.S. Ser. Nos. 09/230594 filed Aug. 1, 1997, and 09/230776 filed Jul. 29, 1997, and U.S. Pat. No. 6,233,907 (Cook et al.), all of which are incorporated herein by reference in their entirety.
Unfortunately, oxygen scavengers do not always activate on command. This may result from a number of factors, including defective scavenger compositions, inadequate triggering conditions, operator error, or a combination of these or other factors. Conventional scavengers do not themselves visually indicate whether or not they are active. In response to this uncertainty, operators of packaging assembly plants prefer to verify scavenger activity as soon as possible after triggering. The longer a failed triggering attempt remains undiscovered, the more waste and expense is incurred, especially where packaging equipment operates at high speeds.
Prior art methods for verifying oxygen scavenger activity in a low oxygen package involve detecting oxygen concentrations in the package headspace. The measurement cannot take place until after the package has been assembled and equilibrium of oxygen levels established among the headspace, package layers, and package contents. Detection of sufficiently reduced oxygen levels within the headspace allows one to infer successful scavenger activation.
Under this approach, one typically has two options, neither of which is particularly satisfactory. One option is to leave an oxygen indicator in the package headspace after it has been assembled and sealed. For example, Mitsubishi teaches an indicator comprising glucose and methylene blue, encased within a sachet. The sachet is left inside the package after it is sealed. A color change within the sachet indicates the presence of unwanted oxygen.
This approach has several disadvantages, however. Sachets must be attached to the package to avoid their being accidentally ingested by the consumer. Some package contents require a moisture-free storage environment. Yet, in the case of the Mitsubishi glucose/methylene blue indicator, moisture may be required to produce a color change. Also, sachets potentially introduce contaminants or other substances into the package that may be incompatible with its contents or accidentally ingested. For some applications, manufacturers may not want to leave indicators in packages where consumers may misinterpret the information the indicator provides.
Another option is to use probes to measure the gas content within the headspace. One commonly used headspace gas analyzer is available from Mocon Inc. Unfortunately, probes that rely on gas chromatography and other such analytical techniques cannot measure oxygen concentration in vacuum packages, where there is substantially no atmosphere to measure. In all cases, probes require sacrificing the sampled package. They invariably require some sort of device that will penetrate the package and remove a portion of the gas within the headspace. The device inevitably leaves a hole in the package, destroying the integrity of the package.
Measuring headspace oxygen, whether by indicator or invasive probe, has an important additional disadvantage as well. It requires time, often hours, for scavengers seated deep within the walls of MAP materials to consume enough oxygen to affect measurably the oxygen levels in the headspace. This is often further delayed and complicated by out-gassing by package contents (as occurs with foods) or by poor circulation of gasses within the package. Clearly, there remains a need in the art for a significantly faster, less wasteful article and method for verifying oxygen scavenger activity in a package, than the old method that relies on measuring oxygen concentration within the headspace of an already assembled package. The present invention provides such an article and method.
In a first aspect, an article comprises an oxygen scavenger; and an oxygen indicator comprising a luminescent compound; wherein the oxygen scavenger and the oxygen indicator are substantially shielded from sources of oxygen exterior to the article.
In a second aspect, a package comprises a tray comprising a barrier liner, and a tray flange; an oxygen sensitive product disposed on the tray; and a film, disposed over the oxygen sensitive product and adhered to the tray flange, comprising a first layer comprising an oxygen barrier; a second layer comprising an oxygen scavenger; and a third layer comprising an oxygen indicator.
In a third aspect, an article comprises a first layer comprising an adhesive; an oxygen indicator comprising a luminescent compound, the oxygen indicator encapsulated by the adhesive; and a second layer comprising an oxygen barrier.
In a fourth aspect, a method of verifying oxygen scavenging activity by an oxygen scavenger comprises providing a solid article comprising an oxygen scavenger and an oxygen indicator, the oxygen indicator comprising a luminescent compound shielded from oxygen outside the article; triggering the oxygen scavenging activity of the oxygen scavenger; exposing the oxygen indicator to the excitation frequency of the luminescent compound; and detecting luminescence by the oxygen indicator as an indication of oxygen scavenging activity by the oxygen scavenger.
In a fifth aspect, a method of verifying oxygen scavenging activity by an oxygen scavenger comprises providing a solid article comprising an oxygen scavenger and having dissolved oxygen; placing a patch comprising an oxygen indicator, comprising a luminescent compound shielded from oxygen outside the article, proximate to the solid article; exposing the oxygen indicator to the excitation frequency of the luminescent compound; and detecting luminescence by the oxygen indicator as an indication of oxygen scavenging activity by the oxygen scavenger.